1. Field of the Invention
The present invention relates to a measurement device, and particularly to a measurement device for simultaneously detecting material level and temperature.
2. Description of the Related Art
For management of bulk material stored in a silo, a measurement device for detecting material level is very important. The material level means a height of the material in the silo, and the material level can be converted to obtain the amount of the material stored in the silo. The measurement device can be applied to petrochemical industry, food industry, feed industry, steel industry, cement industry, etc. Materials stored in a silo may be solid, liquid, or liquid-solid mixture. For example, the materials may be petroleum, coal, iron sand, cement, flour, cattle fat, etc. When each material is stored in a silo, temperature, moisture and an amount of the material will influence the quality of the materials. In some particular industries, when the temperature of the material stored in the silo is not properly controlled, a dry and dusty material may cause a dust explosion.
A conventional measurement device can only detect temperature, moisture, or material level of the material. When a user wants to simultaneously detect the temperature, moisture and material level, the user needs to build a system composed of multiple measurement devices for respectively sensing the temperature, the moisture, and the material level. Then the user can monitor the temperature, the moisture and the material level of the material stored in the silo.
Furthermore, the measurement device can detect the material level by radio frequency (RF) admittance. The measurement device provides a particular voltage to an electrode of the measurement device and detects difference of currents between the electrode and the earth caused by material capacitance. Then the measurement device can calculate the material level by the RF admittance according to a known dielectric constant of the material and the difference of currents between the electrode and the earth.
The dielectric constant of material will change with the temperature of the material. Different temperatures of the material correspond to different dielectric constants respectively. The dielectric constant can be converted to the material capacitance. The material capacitance is an important parameter when calculating the material level by the RF admittance. If the material capacitance of the material is not correct, a calculation of the material level by the RF admittance will have an error. Therefore, the measurement device needs to be further improved.